Technical Abstract:
Garlic mustard (Alliaria petiolata (M. Bieb.) Cavara and Grande) invades and degrades woodland habitats in North America. Coupled-plant herbivore population models will be helpful in the design and implementation of effective biological control strategies for this species. Such models will be most useful if they allow for nonlinearity in demographic rates. However, current data on garlic mustard demography either ignores nonlinear relationships between population density and demographic rates, or treats population density as a categorical, rather than continuous, variable. A quadrat charting method was used to follow the fates of individual rosettes to reproductive maturity, measuring survival and fecundity. Logistic regression was then applied to the data to quantify how these parameters were affected by the population density of individuals binned within varying distances from each plant, in turn. The results of logistic regression indicated that all plants within a 0.25 m2 quadrat were important in determining density dependent dynamics, therefore plant fate data were pooled within quadrats and quadrat-level rates were analyzed in relation to quadrat-level population density. Seedling survival to the rosette stage, rosette survival to reproductive maturity and fecundity were all found to fit negative exponential decay models at P<0.05. These functional relationships will be used to drive coupled plant-herbivore models of garlic mustard biocontrol.